National security adviser Susan Rice warned that, barring American intervention, Syrian strongman Bashar al-Assad will use chemical weapons “again and again” and spread them beyond the country’s borders. A failure to act would increase instability in the Middle East, she said, adding that the strikes are part of the Obama administration’s larger strategy, which is aimed at producing a “negotiated political settlement” that removes Assad from power.

“The likelihood that left unchecked Assad will continue to use these weapons again and again takes the conflict to an entirely different level by terrorizing civilians, creating even greater refugee flows, and raising the risk that deadly chemicals would spill across borders into neighboring Turkey, Jordan, Lebanon, and Iraq,​” Rice said during a speech at the New America Foundation on Monday. She also said that a failure to act would endanger Israel, “where people, once again, have readied gas masks.”

Rice is set to brief lawmakers on the situation in Syria on Tuesday, the anniversary of the September 11, 2012 attack in Benghazi, Libya that resulted in the deaths of four Americans. Then serving as America’s ambassador to the United Nations, Rice falsely blamed the attack on an anti-Muslim YouTube video.